Welcome to LLVM on Windows! This document only covers LLVM on Windows using
Visual Studio, not mingw or cygwin. In order to get started, you first need to
know some basic information.

There are many different projects that compose LLVM. The first is the LLVM
suite. This contains all of the tools, libraries, and header files needed to
use LLVM. It contains an assembler, disassembler,
bitcode analyzer and bitcode optimizer. It also contains a test suite that can
be used to test the LLVM tools.

Another useful project on Windows is Clang.
Clang is a C family ([Objective]C/C++) compiler. Clang mostly works on
Windows, but does not currently understand all of the Microsoft extensions
to C and C++. Because of this, clang cannot parse the C++ standard library
included with Visual Studio, nor parts of the Windows Platform SDK. However,
most standard C programs do compile. Clang can be used to emit bitcode,
directly emit object files or even linked executables using Visual Studio’s
link.exe.

The large LLVM test suite cannot be run on the Visual Studio port at this
time.

Most of the tools build and work. bugpoint does build, but does
not work.

Once CMake is installed then the simplest way is to just start the
CMake GUI, select the directory where you have LLVM extracted to, and
the default options should all be fine. One option you may really
want to change, regardless of anything else, might be the
CMAKE_INSTALL_PREFIX setting to select a directory to INSTALL to
once compiling is complete, although installation is not mandatory for
using LLVM. Another important option is LLVM_TARGETS_TO_BUILD,
which controls the LLVM target architectures that are included on the
build.

See the LLVM CMake guide for detailed information about
how to configure the LLVM build.

CMake generates project files for all build types. To select a specific
build type, use the Configuration manager from the VS IDE or the
/property:Configuration command line option when using MSBuild.

Start Visual Studio

In the directory you created the project files will have an llvm.sln
file, just double-click on that to open Visual Studio.

Build the LLVM Suite:

The projects may still be built individually, but to build them all do
not just select all of them in batch build (as some are meant as
configuration projects), but rather select and build just the
ALL_BUILD project to build everything, or the INSTALL project,
which first builds the ALL_BUILD project, then installs the LLVM
headers, libs, and other useful things to the directory set by the
CMAKE_INSTALL_PREFIX setting when you first configured CMake.

The Fibonacci project is a sample program that uses the JIT. Modify the
project’s debugging properties to provide a numeric command line argument
or run it from the command line. The program will print the
corresponding fibonacci value.

Test LLVM in Visual Studio:

If %PATH% does not contain GnuWin32, you may specify
LLVM_LIT_TOOLS_DIR on CMake for the path to GnuWin32.

You can run LLVM tests by merely building the project “check”. The test
results will be shown in the VS output window.

Test LLVM on the command line:

The LLVM tests can be run by changing directory to the llvm source
directory and running:

This example assumes that Python is in your PATH variable, you
have built a Win32 Debug version of llvm with a standard out of
line build. You should not see any unexpected failures, but will
see many unsupported tests and expected failures.

This will create the result file hello.bc which is the LLVM bitcode
that corresponds the compiled program and the library facilities that
it required. You can execute this file directly using lli tool,
compile it to native assembly with the llc, optimize or analyze it
further with the opt tool, etc.

Alternatively you can directly output an executable with clang with:

C:\..>clang hello.c -o hello.exe

The -ohello.exe is required because clang currently outputs a.out
when neither -o nor -c are given.

This document is just an introduction to how to use LLVM to do some simple
things... there are many more interesting and complicated things that you can
do that aren’t documented here (but we’ll gladly accept a patch if you want to
write something up!). For more information about LLVM, check out: